1. Field of the Invention
This invention relates to gastrointestinal disorders. More particularly, this invention relates to treatment of gastrointestinal disorders by using a method and apparatus for providing electrical stimulation of the gastrointestinal tract.
2. General Background and State of the Art
The reception of nutrition in the human body is an essential step of the digestive process which is performed by the gastrointestinal tract. An important element in the digestive process is gastric and intestinal peristalsis, the coordinated and locally controlled contractions that propel food and wastes through the various stages of digestion and excretion. Peristalsis is accomplished through a coordinated combination of mechanical, electrical, chemical, and hormonal mediation.
Gastroparesis is a chronic disorder of the stomach, defined as delayed gastric emptying of a solid meal. Symptoms of gastroparesis range from early satiety and nausea in mild causes to chronic vomiting, dehydration, and nutritional compromise in severe cases. A series of experimental studies in various animal models has described various loci and patterns of electrical stimulation that might be capable of producing the desired gastrointestinal contractions in patients with conditions such as gastroplegia (stomach paralysis) or gastroparesis (stomach weakness). The more common forms of human gastroparesis, for example, appear to be associated with loss of the vagal innervation of the stomach, which should leave intact the intrinsic sympathetic circuitry within the stomach walls that coordinates peristalsis.
Thus, one or a small number of stimulation channels should be effective in stimulating activity initiated in the gastric pacemaker. However, the previously available technology for electrical stimulation makes it difficult even to conduct research in human subjects, much less to provide them with a long term treatment. Most of the studies have employed short-term percutaneous leads. The scientific literature includes descriptions of clinical experiments, but the experimental designs have been compromised by the limitations of the available technology and the results are inconclusive.
Previously available implantable clinical stimulators as described, for example, in U.S. Pat. Nos. 5,861,014 and 5,995,872, require electrical leads to conduct stimulation pulses from a relatively large electrical pulse generator to electrodes affixed to the desired stimulation site. However, the large amount of motion between the stomach and adjacent structures makes it impractical to maintain such leads.
At the other end of the gastrointestinal tract, similar disorders of peristalsis result in constipation or retention of feces in the colon and rectum. Conversely, excessive motility of the colon leads to diarrhea and clinical disorders such as colitis and “dumping syndrome” in which patients are unable to retain food in their gastrointestinal tracts long enough for proper digestion and absorption. Neuroscientists believe that various parasympathetic and sympathetic neural circuits exist to initiate or inhibit the natural peristalsis rhythm generators within the walls of the colorectal system. Electrical stimulation applied in the vicinity of these neurons could be used to activate such circuits and restore the desired level of motility, much as a cardiac pacemaker maintains regular beating of the heart.